This invention relates to improvements in optical assemblies of the type commonly employed in photoelectric beam systems, sometimes known as "electric eye" systems.
The so-called "electric eye" is a photoelectric control system which typically comprises two photoelectric components. One component functions to produce and transmit a narrow beam of light, or some other form of electromagnetic radiation, across a space in which some event will occur which will somehow affect the intensity of the beam at remote position. The other component is positioned at the remote position to be irradiated by the beam and functions to sense the intensity of the beam and to provide some indication in the event the level of irradiation drops below or increases beyond a certain level. Both components typically comprise an optical system of some sort which serves either to collimate radiation emanating from a source (e.g., a light-emitting diode) or, alternatively, to focus received radiation on a radiation-sensitive element (e.g., a photodiode).
To maximize the sensitivity of photoelectric beam systems, the respective optical axes of the two spaced optical systems must be coincident. Since it is rarely possible in the field to mount the two components on a support such that the optical systems are perfectly aligned, it is common to provide in each optical system some means for adjusting the position of the optical axis relative to a supporting housing. Typically, a pivotally mounted reflective element is incorporated in each optical system to facilitate optical alignment. See, for instance, the mirror arrangement disclosed in U.S. Pat. No. 3,752,978. Using an adjustable mirror element enables the refractive element or elements to remain stationary and always focused upon the source of radiation or the radiation-sensitive element. However, there are certain disadvantages in using a separate adjustment mirror. For instance, the mirror itself represents additional manufacturing costs, it reduces system sensitivity due to its inherent optical losses, and it reduces alignment stability by doubling any angular displacement between the beam of radiation and the optical axis.